Sharpening Part 18 – The Nagura Stone

A Tsushima Black Nagura stone 55x55x55mm

In the previous article in this series your unworthy servant listed some of the tools and accouterments necessary for sharpening Japanese tools using waterstones. In this article we will examine one especially useful stone mentioned previously: the Nagura. I know, it sounds like the name of some evil thing that crawled out of a mountain cave in Angmar in Middle Earth, but if you don’t have this little stone, you should get one.

The Nagura Stone

Nagura stones have been used in Japan for millennia, but they are not unique to Japan. For instance, the Coticule stones of Northern Europe have been used with nagura-equivalent stones since before Roman times. And I would not be surprised if the same tradition existed elsewhere too, they are so useful.

Mikawa Nagura Stone

There are several varieties of Nagura stones mined in Japan, the two most popular being the grey/black Tsushima stone pictured above and the softer white Mikawa stone pictured below. I use a soft white Mikawa Nagura stone for my straight razor.

The black Tsushima variety is cut from sedimentary stone on the ocean floor near Tsushima in Nagasaki Prefecture, located midway between Japan’s Kyushu island and South Korea. I believe it to be the best for general usage so I will discuss this stone in particular.

Like all Japanese natural stones, Tsushima Black Nagura are mined from sedimentary deposits created by airborne volcanic ash being sifted by distance and wind and filtered by waves and tides by the time they reach the ocean floor. But they have not been subjected to the metamorphic weight and heat that makes harder stones, and are relatively soft and permeable. They also tend to crack in the same plane they were laid down in, especially if subjected to wet/dry and/ or freeze/ thaw cycles, so special measures are necessary to protect them.

The Job of the Nagura Stone

The Nagura stone is typically used to perform five tasks.

1. Cleaning Finishing Stones: Finishing stones always become contaminated with pixie dust and grit from rougher stones. A 10,000 grit stone with 1,000 grit particles mixed in is much less than 10,000 grit effective. If you think a stone is contaminated, wash it well with a scrub brush and clean water then work the surface with a clean Nagura stone to loosen and float up the contaminate particles, then wash off the slurry. The stone will be clean.

2. Removing Clogging: Similar to 1 above, the Nagura stone is effective at unclogging dried slurry and metal swarth from the sharpening stone’s surface helping it get back to work sooner.

3. Truing Stone Surfaces: Finishing Stones need to be trued occasionally, usually the corners and edges. Use the Nagura periodically to knock these high spots down. The resulting slurry can be used for your normal sharpening process without it all going to waste. This is wisdom.

4. Reducing Startup Time: Time is money. Waterstones abrade most efficiently when they have a slurry worked up, but it can take time to get decent slurry started on some stones, especially hard ones, and with some blades, especially those with soft jigane. Use the Nagura to quickly bring up this necessary slurry saving time and money. If you focus on the corners and perimeter of your stones, which tend to be high anyway, it will contribute to truing the stone as mentioned in 2 above.

5. Reducing the Average Particle Size in the Slurry: Nagura grit is quite fine. You can add Nagura slurry to a stone (by rubbing the stone to create slurry at corners and edges, BTW) to reduce the average grit size of the slurry making a stone create finer scratches and a better polish on your blades. For instance, adding Nagura slurry to a 8,000 grit stone makes it function more like a 9,000-10,000 grit natural stone without the bulk and weight of an additional full-size stone.

Using the Nagura Stone

Nagura stones are just as useful when sharpening with synthetic sharpening stones as they are with natural stones. In fact, they may be even more useful with synthetic stones since they tend to be harder and synthetic stone slurry containing nagura particles more closely approximates the performance of natural stones.

Nagura stones are easy to use. Simply wet the large stone and rub the small stone on its surface. You may need to add additional drops of clean water while doing this. The goal is to wear down the high spots on the large stone while at the same time producing a slurry mixture from both stones to use when sharpening blades.

The key is to pay attention, use your handy dandy stainless steel ruler to identify the high spots, maybe mark them with a pencil, and use the nagura on those areas first. Don’t be a ninny and rub the nagura all over the stone willy nilly like you’re washing your pet goat. Make a plan. Work the plan. Develop good habits and speed will follow.

If the large stone is already perfectly flat, and you need to produce a starting slurry, work the ends and corners of the large stone with the nagura in anticipation of those areas becoming high in the near future. That’s a good boy.

Protecting the Tsushima Nagura Stone

Nagura stones are fragile. To avoid water penetration between the sedimentary layers and the cracks that may result, it is wise to use the side of the stone that was in a horizontal plane when it was formed. It is also wisdom to use only one surface of the stone and to coat the stone’s other 5 sides with paint to prevent water infiltration and cracking, and to keep skin oils from penetrating. Traditionally, natural urushi lacquer made from an irritating tree sap has been used for this purpose in Japan, but any high-solids urethane will do the job.

The Nagura stone is a subtle tool. As your sharpening skills improve the value of this tool will become apparent.

In the next article in this depraved series about sex, drugs and goat washing, we will discuss ways to maintain sharpening stones. Some people will be miffed. Others will be thrilled. Goats will be indifferent. What about you?


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19 thoughts on “Sharpening Part 18 – The Nagura Stone

  1. Again, a really informative post Stan!! I have a few Nagura but all of them in the “white” colour…. Maybe I need to get one of the black one like you suggest!! I will look into it!
    Thank you
    It is officially the new year in your neck of the wood!! Have the greatest of year for 2020!!


  2. Thanks, Henk. I have tried it, and prefer the nagura. I don’t want a rougher surface on my sharpening stones, effectively reducing the degree of polish it can accomplish until it becomes smooth again. I don’t want to wear out expensive diamond plates to abrade stone instead of the steel I need them to abrade.

    Liked by 1 person

    1. So I assume you use the 3 stones technique to keep your stones flat!?!
      What do you do with the expensive natural stones, having 3 of each seems expensive?


  3. No, just 2 stones each of the 1,000 and 2,000 grit (and carborundum stone sometimes).

    I use the Nagura, and very occasionally (once a year?) the glass plate to true my finishing stones.

    Henk, if I may be so bold as speak for him (we have argued about this by email several times), prefers to use a diamond plate to true all his stones because it is quick and does a good job. He is right, except perhaps about the good job part, which is where we disagree.

    I think diamond plates are too expensive to use on sharpening stones because sharpening stone grit, while softer and less abrasive than diamond dust, is a lot harder than steel and wears the diamond plates out prematurely. I don’t consider that cost-effective. On the other hand, Henk uses his tools professionally, and time is money, so the greater speed of diamond plates may justify wearing them out sooner.

    Diamond plates also dig striations in the stone’s surface that make the stone of effectively rougher grit until the stone’s surface wears smooth again. The same exact thing is true when using a rougher stone to smooth a finer stone. How much rougher? It varies, but the difference in polish is clearly visible, and the time that must be spent on the next stone in the series is correspondingly longer, in my experience. This is why I prefer to use the same grit stone to true each stone.

    By using the same grit stone, I can true a stone while I am using it, without having to worry about grit (or diamond particle) contamination, which I have experienced with diamond plates but which Henk says doesn’t happen anymore. He may be right, I don’t know.

    As I mentioned in the post, by having 2 each of my most abrasive and hardworking stones close at hand, I start the workday with 4 flat, true sharpening surfaces, and don’t need to worry about flattening them until all four are dished. In my little workshop, I just work on one side of each stone, but when 2 stones become hollowed out, then I rub them together to true them. It is quick and easy and economical and the stones don’t contaminate each other.

    This is the traditional way. Is it the quickest? No. Is it the cheapest? Yes. Is it the best? Idunno. Maybe. It works pretty good.


    Liked by 1 person

    1. Makes a lot of sense, to ma anyway!! I’m like Henk, I use Atoma diamond plate to flatten my stones…. I thought you needed 3 stone to make sure you end up with totally flat stones!! I’m considering going to the stone to stone method… I need to get more stones hahaha. I never use diamond plate for anything else than flattening my water stone…. And they don’t last that long and are not always as flat as people think they are!! So I’m sure a stone to stone system is more efficient in the long run!
      Sorry Henk I’m going with Stan!!


  4. The only way to get stones perfectly flat is to use superflat ceramic lapping plates and fine powders. You can’t do it with a diamond plate or another stone.

    The float-glass plate I recommend is the closest economical method I know. Indeed, it tends to make stones convex in two axis, which is not a bad thing within limits.

    But a perfectly flat stone is expensive to maintain and not especially better for general woodworking than a pretty-flat stone. The rabbit-hole is not only deep, but sleepless nights and gibbering insanity await those who reach the bottom. Beware!

    Liked by 1 person

    1. Rabbit hole indeed!! I have a friend that compete in the shaving things you know the one at Kez…. Well it is an obsession and one that I almost got caught into, but I use my tools for a living and I can’t just fall in that kind of “craziness” hahaha.

      I’m pretty happy with my sharpening, especially in the last few months! But still lots to learn especially when it comes to finish surface, I hate to sand, so kanna finish is what I’m after and I’m there most of the time on smaller surfaces in easier wood…. But larger surface and trickier wood I’m still inconsistent.

      I really like the conversation here, You and Henk disagree with respect!!


      1. So you know that rabbit hole then.

        Large surfaces with grain all over the place are difficult even for the very best. I could once hold my own, but that was many years ago when I used a plane everyday. You really have to stay on top of the dai.

        Sharp will only get you so far. Work on the dai and blade combination.

        Henk is a good man. I have not met him or seen his work in person, but he has shown me pictures. He knows what he is doing, and got excellent instruction from Japanese craftsmen back when. Everyone’s approach to tools and woodworking will be a little different.

        Liked by 2 people

  5. Stan, there was no option to reply to your last post/reply, so here it is! Indeed the dai tuning/conditioning is critical and man does it make a difference!! Still not the best at it and maybe a bit shy sometime scared to wear them out and have to cut an other dai(something I’ve done only once so far!).

    On an other topic, bevel angle, all the plane blades seems to come in at 25 degrees… I find that angle to be almost useless… So I regrind them(after using them a bit to see if I can work with it) to 28-30 degrees and seems to have a lot more success with that… But that is a lot of work and sometime lots of taping…. I wonder why the smith do it that way and not make it right away to 27-28* where from what I read seems to be where most carpenter/woodworker like to have there tools at?


  6. David:

    Yes, new planes delivered with too shallow a bevel angle is a problem even for me. Blacksmiths are focused on making the blade and getting it out the door to the dai maker. Sadly, small details like bevel angle sometimes get overlooked. Professional sharpeners will do the same thing if you let them. But all I can do is scold them and ask them to do better next time.

    Please don’t grind your plane blade. It deserves better treatment than that.

    This is one of the few situations where using a honing jig like the Lie-Nielson widget or cheaper Eclipse knock-off makes perfect sense. With the blade locked into a jig at the right angle you can put it on your stones at the correct bevel angle to make a small secondary bevel (something I vehemently oppose in most any other circumstance).

    By using the sharpening jig at the same angle for a few more sharpening sessions, the bevel will gradually get wider a little at a time without wasting expensive steel or creating an evil rounded bevel. You will need to use the jig for a while, but eventually enough of the flat bevel will be established so you can stop using the jig and get back to freehand sharpening as the good Lord intended.

    Don’t let using a jig become a habit for normal sharpening, though. It’s very embarrassing. That would be like using a wheelchair to keep your shoes from wearing out: your shoes will look great but eventually you won’t be able to get around without it. Sooo embarrassing.


    1. I already do this… not to that extend or should I say I use to do that before being comfortable with the low speed grinder…. maybe I go back that way… I hate the grinder but it is so quick and so far I never ruined a blade..

      Regarding sharpening jigs, what about the Japanese models? Or the sharp skate one?


      1. I guess I’ll reply to my own post cause there is no option to reply to yours… I have the Veritas MKII and it is a good guide, but not so good with J tools because of the shape of the blades… As for Sharp skate, I can get one for a good price since Harellson Stanley offered me a deal a while back, maybe I will take him on it!!
        I have an original eclipse made in England but have a hard time to make it work properly!


      2. The richard kell always intrigued me, so simple!! I just pull the plug on a sharp skate and we’ll see how it does!! Yesterday I change the bevel angle on my Yamamoto Guren 58mm and I used the Veritas MKII It went well, but it took some time on my 400grit water stone(hibiki I think, light green) anyway it is now at around 28 degrees I believe, and should last better! I have an other one to do today, a 70mm that will be a bit longer I guess!!
        Thank you again for the great communication and exchange! You hold a great blog, long life!


  7. Hi Stan,
    Thank you for making me realize what I was seeing was grit contamination.
    I am in the process of getting a black tsushima nagura stone from a Japanese retailer, but he says the grit is around 3000, it looks very much like yours. Is this what you use for your 10k stone? And do you also use it for slurry on 8k and 10k?


    Liked by 1 person

    1. You are welcome. Contamination is always a risk. Yes, what I use and recommend is the black Tsushima Nagura, although a white Mikawa Nagura, while softer, works too. I can’t speak to the grit or the suitability to your purpose of the particular stone you are currently considering purchasing because it is a natural stone, an item that naturally entails some uncertainty.


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